Plasticized polystyrene-type resins



Patented May 28, 1946 I PATENT orrlcs PLASTICIZED POLYSTYRENE-TYBE RESINS Frank J. Soday, Baton Rouge, assignor to The United Gas Improvement Companna corpora 1 tion of Pennsylvania Serial No. 521,709

No Drawing. Application February 1944, 5

12 Claims.

This invention relates to new compositions of matter comprising polystyrene-type resins and certain high-boiling esters.

More particularly, this invention pertains to resinous compositions comprising one or more resins derived by the polymerization or copolymerization of one or morecompounds selected from a list comprising styrene and substituted styrene and at least one plasticlzing agent selected from a list comprising cyclohexyl naphthenate and cyclohexyl stearate.

An object of the invention is to provide resinous compositions which have been plasticized sufllciently to impart a substantial degree of flexibility thereto. Another object of the invention is the provision of molding compositions possessing improved flowing properties at elevated temperatures. A iurther object of the invention is the provision or a casting composition comprising monomeric and/or partially polymerized styrene and/ or substituted styrene containing one or more esters of the type described adapted for the production of castings or other formed-objects, particularly objects containing metallic or other inserts. Other objects and advantages of the invention will be apparent to those skilled in the art upon an inspection of the specification and claims.

Styrene, or substituted styrenesconiorming to i the following formula I in which a, b, and each may represent hydrogen, halogen, or alkyl, (1 may be halogen or alkyl, and n may be any integer from 0 to 5, may be polymerized to form light-colored, or colorless, resins possesslng excellent physical properties. Examples of alkyl groups are methyl, ethyl, propyi, butyl and amyl,

This applies particularly to styrene and to nuclearly substituted styrenes in which the substituent or substituents are halogen or alkyl groups, and especially when the substituents on the nucleus are less than three. In any case, each alkyl-grougi preferably contains less than 6- carbon atoms.

In many cases mono-substitution, either on the ring or on the side chain is preferred.

Examples of substituted styrenes which are (cl. gee-sol particularly well adapted to the production of resins of this typ are the nuclear-substituted methyl styrenes, such as m-methyl styrene, pmethyl styrene, and o-methyl styrene. -5 Particularly desirable resins are obtained by the copolymerlzation of mixtures of meta methyl styrene, para methyl styrene, and ortho methyl styrene in which meta methyl styrene and para methyl styrene are each present in proportions in substantially greater than that of ortho methyl styrene. Excellent results are obtained when the preponderating unsaturated hydrocarbon present in the mixture to be polymerized is meta methyl styrene, followed by para methyl styrene l5 and ortho methyl styrene, in \the order given.

Good results may be obtained when the preponderating unsaturated hydrocarbon present is para methyl styrene, followed by meta methyl styrene a and ortho methyl styrene in the order given. Copolymers possessing excellent surface hardness characteristics, as well as other desirable properties may be prepared by the polymerization of a mixture of nuclear-substituted methyl styrenes containingtrom 55 to 75% meta methyl styrene, from 20 to 45% para methyl styrene, and from 1 to 10% ortho methyl styrene.

Polymers possessing unusually good physical properties also may be obtained by the copolymerization of styrene with one or more substituted styrenes, such as the nuclear-substituted methyl styrenes.

Resinous' materials possessing very desirous properties may be obtained by mixing polystyrene with one or more polymers obtained from substituted styrenes, such as the nuclear-substituted styrenes. Substituted styrene polymers obtained by the polymerization of a mixture of meta, para, and ortho methyl styrenes. in which the meta isomer predominates, are preferred.

40 For many uses, however, I have found that the foregoing resinsdo not possess satisfactory elastic characteristics. Thus, for example, the use of polystyrene, polymethylstyrene, styrenemethyl styrene copolymars, and/or polystyrene-polymethylstyrene mixtures for the preparation or castings or molded objects containing metallic, or other, inserts, has given unsatisfactory results in certain cases.

Thus, for example, the molding or casting may develop cracks around the metallic insert, resulting in a definite reduction in the mechanical strength, and other properties, of the unit.

This is particularly undesirable in the case of certain electrical units, such as condensers, con- 66 ductors, and the like, where the formation of cracks in the cast or molded object may result in undesirable electrical phenomena, such as corona discharges. In the case of radio and television condensers imbedded in polystyrene or polystyrene-type plastics, the formation oi corona discharges in cracks formed in the plastic mass largely interfere with the operation of the unit, and may render it entirely unsuited for this type of work.

In addition, the formation of cracks in the plastic mass in which condensers, or similar units, are imbedded may permit moisture to penetrate the unit, thus impairing its emciency and rendering it unsuited ior certain applications.

1 have discovered that the formation of cracks in polystyrene type plastics may be retarded or completely eliminated, and certain of the other physical properties 01 the material improved, by the incorporation therein of at least one ester the character herein set forth.

Esters which have been iound to be particularly good plasticizing agents or polystyrene-type plastics are'the cyciohexyl esters, such as cyclohexyl stearate and cyclohexyl naphthenat e.

It is to be understood, of course, that one or more esters or the type described may be emplayed, as well as mixtures of one or more esters of the type described in conjunction with the use oi one or more plasticizing agents of other types, such as the chlorinated diphenyls,

Any desired proportion of plasticizing agent of the type described herein may be employed, although one should be taken not to exceed the compatibility limits of the plasticizing agent, or agents, selected and the polystyrene-type plastic. For many purposes I have found that 10% or even less, of plasticizing agent is sufficient to impart the desired flexibility, as well as other desired properties such as freedom from cracking or checking, to the polystyrene-type plastic. Higher proportions may, of course, be used if desired. I prefer to employ from 1% to 30%, and more preferably from 5% to 20%. Plasticizing agent based on the weight of the polymer.

Esters oi the type described may be added to the plastic at any stage of its preparation, such as before, during, and/or after polymerization. Thus the esters, or mixtures of esters, may be added to the monomeric styrene and/or substituted styrene prior to, or during, the polymerizetion thereof, leading to the production oi a polymer or copolymer through which the plasticixing agent has been uniformly distributed. This is particularly desirable from the standpoint of the production of castings. Such castings may, of course, contain metallic, or other desired inserts.

0n the other hand, a plasticising agent of the type described may be added to the polystyrenetype plastic at any stage subsequent to the polymerization thereof. The plasticizing agent may be added in any desired manner, such as by masticating a mixture of the plastic and plasticizing agent on hot rolls until a uniform blend has been achieved. Another method comprises the addition of the plasticizing agent to a solution of the plastic in a suitable solvent, followed by removing the solvent, if desired, by any suitable method. This may involve distillation, which may be assisted by the use of steam and/or reduced pressures, working on hot rolls, spray drying. and the like The plasticised product then may be further processed, ii desired. Thus, it may be subdivided to term a molding powder, or it may be extruded to form rods, tubes, toil, film, and other shapes.

omma Other ingredients also may be incorporated in the polystyrene-type plastic prior to, during, or after the addition of plasticizing agents of the type described herein, and such additions may be made prior to, during, or after the formation of the plastic. These additional ingredients may include one or more agents selected from a list comprising dyes, pigments, fillers, other plasticizing agents, rubber, both natural and synthetic, and other resinous and/or plastic materials.

The polymerization oi the styrene or substituted styrenes employed in the preparation of plastic compositions of the type described herein may be carried out in any desired manner, such as by the application of heat. In addition, certain catalytic agents also may be employed, either alone or in conJunction with the simultaneous, or otherwise, application of heat. Examples of suitable catalytic agents are peroxides, such as hydrogen peroxide, benzoyl peroxide, and the like, metallic halides, metallic halide-organic solvent complexes, and contact agents such as clay, activated clay, alumina, silica gel, and the like.

The advantages to be obtained by the use of my plasticizing agents over those used heretofore may be illustrated by the following examples.

Example 1 A mixture of 5 parts of dibutoxyethyl phthalate and 95 parts of monomeric styrene was placed in a' cylindrical container, after which an aluminum rod V4" in diameter and sufliciently long to pro- Ject above the surface or the monomeric styrene, also was placed in the container. The monomeric styrene then was polymerized by heating for 72 hours at C., 48 hours at C. and 20 hours at 65 C.

Upon removing the polystyrene casting containing the metallic insert from the container, and permitting it to stand overnight, definite signs of cracking were observed. The majority of these cracks originated'on the surface of the metallic insert within the casting and penetrated the plastic mass for considerable distances. At the end of one week's storage, the casting was cracked to an extent sumcient to render it useless for any commercial application.

The experiment was repeated, using a number of other commercial plasticizing agents, with the following results.

In addition to cracking, the majority oi the piasticized castings listed showed excessive blushing, crazing, checking, pitting, or other surface imperfections after the indicated storage periods.

The following experiments will serve to illustrate the greatly improved results to be obtained by the use of esters of the type described herein as plasticizing agents for polystyrene-type plastics.

Example 2 A casting similar to that obtained in Example l was prepared bythe polymerisation of a mixture or parts or cyclohexyl naphthenate'and 95 parts of monomeric styrene.

The plasticized casting was colorless, transparent, andentirely free from surface, or other imperi'ections after a storage period of 27 months.

Example 3 This was a repetition of Example 2, with the exception that a mixture of 5"parts oi cyclohexyl stearate and 95 parts of monomeric styrene was employed in the preparation or the casting.

The plasticized casting was entirely free from cracking and other imperfections after a very extended. storage period.

Example 4 Polymethyl styrene plasticized by the addition or 5% cyclohexyl naphthenate is extruded in the form or a rod under a pressure of 2500 pounds per square inch and a temperature of 150 C. The rod obtained possesses good surface characteristics and excellent mechanical properties.

Example 6 A styrene-methyl styrene coploymer plasticized by the addition or 5% cyclohexyl napthenate is molded at a temperature of 180 C. and a pressure of 1800 pounds per square inch. A molded methyl styrene and a plasticizing agent selected from the group consisting of cyclohexyl naphthenate and cyclohexyl stearate.

2. A plastic composition comprising polystyrene and a plasticizing agent selected from the group consisting of cyclohexyl naphthenate and cyclohcxyi stearate.

3. A plastic composition comprising polymerized nuclear substituted methyl styrene and a plasticizing agent selected from the group consisting of cyclohexyl naphthenate and cyclohexyl 'stearate.

.4. A plastic composition comprising a styrenenuclear substituted methyl styrene copolymer and a plasticizing agent selected from the group consisting of cyclohexyl naphthenate and cyclohexyl stearate.

5. A molded object prepared from polystyrene plasticized with av compound selected from the group consisting of cyclohexyl naphthenate and cyclohexyl stearate.

6. An extruded polystyrene object prepared from polystyrene plasticized with a compound selected from the group consisting of cyclohexyi naphthenate anad cyclohexyl stearate.

'7. As an article of manufacture, a polystyrene casting containing a metallic insert and a pissticizing agent selected from the group consistobject exactly reproducing the interior of the mold and possessing excellent mechanical properties is obtained.

ing or cyclohexyl naphthenate and cyclohexyl stearate.

8. As a new article of manufacture, a poly methyistyrene casting containing a metallic insert and a .plasticizing agent selected from the group consisting of cyclohexyl naphthenate and cyclohexyl stearate.

9. An electrical condenser imbedded in polystyrene containing a plasticizing agent selected from the group consisting of cyclohexyl naphthenate and cyclohexyl stearate.

10. An electrical conductor imbedded in polystyrene containing a plasticizing agent selected from the group consisting of cyclohexyl naphthenate and cyclohexyl stearate.

11. A molded object prepared from polymethylstyrene plasticised with a compound selected from the group consisting oi. cyclohexyl naphthenate and cyclohexyl stearate.

12. An extruded polymethylstyrene object prepared i'rom polymethylstyrene plasticized with a compound selected from the group consisting of cyciohexyl naphthenate and cyclohexyl stearate.

FRANK J. SODAY. 

